This invention relates to a stable control solution for the determination of urobilinogen.
Urobilinogen is a reduction product of bilirubin which, in turn, is a breakdown product of heme. The latter substance is formed primarily from the degradation of the red blood cells (erythrocytes). The red blood cells contain hemoglobin which captures and holds oxygen for transfer to all the cells of the body. Hemoglobin also binds in a different way some of the carbon dioxide made in the body. The carbon dioxide is vented out in the lungs when the red blood cells pick up a new amount of oxygen for redistribution to the body.
The red blood cells are made in the bone marrow and since they have no nuclei they have a finite life of usefulness in the body. The average life of a red blood cell is about 120 days. At the end of this time, the reticuloendothelial (RE) cells in the liver proceed to engulf and destroy the old red blood cells whereby hemoglobin is released into the environment of the RE cells.
The hemoglobin molecule consists of the red heme pigment and a protein called globin. The heme pigment is made up of iron and a cyclic tetrapyrrole known as porphyrin. The porphyrin ring opens up by enzaymatic action and forms a green pigment referred to as biliverdin which is then further reduced by enzymatic action to bilirubin.
Both bilirubin and biliverdin are excreted into the bile ducts, and the bile, in turn, is excreted into the intestines. Some of the bile is adsorbed further down in the small intestine and back into the blood stream. The material adsorbed into the blood stream is further reduced to urobilinogen. Part of this adsorbed material then passes out of the body through the kidneys into the urine as urobilinogen or in an oxidized form as urobilin.
Normally, little or no urobilinogen or bilirubin is excreted in the urine unless a pathological condition exists in the liver such as an impairment of the liver cell mechanisms giving rise to various types of jaundice. Urobilinogen problems are more evident with Orientals and the type of liver damage that they can have than with Caucasians. The determination of urinary urobilinogen also is a useful test for detecting the early stages of hepatitis.
In view of the above, determination of urobilinogen in urine is important in clinical testing and diagnostics. Various so-called reagent strips and dipsticks used for urine testing contain tests for urobilinogen. The commercially available Chemstrip.RTM. of Bio-Dynamics, Division Boehringer Mannheim Corp., Indianapolis, Ind., and the N-Multistix.RTM. of Ames Division, Miles Laboratories, Inc., Elkhart, Ind., are typical examples of such products which include tests for urobilinogen.
The classical test, originally devised by Paul Ehrlich in 1901, employs paradimethylaminobenzaldehyde as a test for urobilinogen which in strongly acid medium produces a brown-orange color with said reagent (Ehrlich's reagent). In modifications of this test, 4-methoxybenzene-diazonium-tetrafluoroborate and related compounds replace Ehrlich's reagent as first described by Kutter et al., Dtsch. Med. Wschr. 98, 112 (1973).
Further background on urobilinogen and its testing can be had by reference to a common text in the field, for example, Tietz, Fundamentals of Clinical Chemistry, W. B. Saunders Company, Philadelphia, Pa., 1970, pp. 762-766. See also, Jackson and Conrad, Amer. Clin. Prod. Rev. 4 (12), 10-19 (1985).
As part of normal quality control, the clinician and laboratory technologist must be assured that the urobilinogen test is working properly; that is, it must give a good positive test if positive material is present in the patient's sample. Otherwise, the clinician could miss a potential problem present in the urine which may be indicative of certain liver malfunctions. Availability of a stable control solution for urobilinogen would this find significant use as an adjunct to the quality control of urobilinogen tests.